The solution is to use clear RTV (silicone rubber compound) to seal the cracks in the lens, thus preventing water from entering the housing and destorying the lamp, reflector and shield.
Of course, you must only have cracks and not large holes in your lens. Also, if water has been inside your housing for a long time, your metal shield has probably rusted away, and you must replace your assembly.
However, if you catch it soon enough after the cracks appear that no rust has occurred, you can remove the assembly from the bumper, and remove the bulb from the assembly, then put the assembly in an oven at 300 degrees for about 10 minutes to expell any moisture inside. Remove carefully and allow the assembly to cool on its own.
When cool, and the inside is free of moisture, clean the face of the lens, then apply a thin, flat bead of clear RTV over the cracks in the glass to seal them. If you have ever used RTV before, you know that it can be somewhat of a pain to work with because it is sticky and it gets everywhere (messy). But not to worry, if you botch up the job, let it dry (cure), then use a sharp razor blade to remove it from the glass. It cuts away easily from smooth surfaces such as glass. Thin films of RTV may be rubbed away with a soft cloth. You may clean up your work, or remove it all and start over. The nicer your job, the less obvious it will be as to what you have done. Re-install into the bumber, and install a new bulb.
The RTV is a high temperature compound and will not be affected by the heat of the lamp. Since the lens is already cracked, it has the "give" needed to releave the thermal expansion stress caused by the heat of the lamp, so it will not crack anymore. The RTV is flexible and has excellent adhesion. It will keep the cracks sealed against entry of moisture, even as the joints in the cracks expand and contract. The clear RTV causes no noticeable reduction in lamp output.
I have both fog lamps repaired using this method. They have over 10 months on them and are doing just fine, and I alway use my fogs with my headlights. You may notice the RTV turning yellow after a couple of months, but using a glass cleaner containing ammonia will clean that right up. Apparently, the yellowing is only on the surface, because after cleaning, it will be as clear as the day you put it on. When cleaning the lamps, I always check for beads of moisture inside, just in case it needs a touch-up, but so far its just fine.
Yes, this fix is not as pretty as nice shiny new lamps without cracks. But to have that, your going to have to keep your bucks flowing to the Fatherland! This fix will keep the inside of your fogs clean and dry and working. And for a $3 small tube of RTV, that's not bad!
PS, I used Permatex Brand Adhesive RTV in clear. I really don't if other brands will work as well or not. I do know that some RTVs smell like vinegar when curing (original type), and some smell like ammonia when curing (new type). I have not been as impressed with the new type over the old type. The brand described above is the old type. Good luck and enjoy your car!
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